Huh! I would have assumed it was written in chat rather than done in a chat dialogue format. After all, we never called it "email fic" that I recall in the pre-chat era even when stories used Internet platform style dialogue.

so basically someone created a fanlore page for something called "text fic", which was news to me! but there's an AO3 tag for chatfic and it's full of characters IM'ing each other. from what melannen says below, this might be Homestuck's fault.

Just a further thought, I suppose it might also depend on the format, even if written in chat. If the chat platform was essentially being used to RP then it would be an RP fic regardless of platform. But I expect the same term could be used for two different things.